The main objective of this study is to further define the pathophysiology of blood pressure elevation in young patients with primary hypertension by testing the hypothesis that central and peripheral noradrenergic hyperactivity is present in a significant number of these patients compared to persons with secondary hypertension and normotensives defective dopaminergic tone is associated with noradrenergic hyperactivity. Psychological testing is included to determine if behavioral characteristics, anxiety or stress reaction patterns are associated with central noradrenergic hyperactivity. In addition, the role of central noradrenergic activity in the regulation of blood pressure in patients with Parkinson's Diseases is studied and the hypothesis that phenytoin lowers blood pressure in man by association with reduced central noradrenergic activity is studied.